This invention relates to a pattern aligning device for a sewing machine for sewing two sheets of material in such manner that patterns on the two sheets of material are aligned during sewing.
A sewing machine of this type has been disclosed in the U.S. Pat. No. 4,612,867 to Rosch et al. In this document, the feed of either the upper or lower feeder is changed with respect to that of the other in accordance with a displacement of a pattern which is determined by processing pattern signals from a pair of pattern sensors. Thus, one of the two sheets of material is moved only in the sewing direction for adjusting the relative positions so that the patterns are correctly aligned.
The prior art sewing machines are able to align such one-dimensional patterns laying transverse to the sewing direction, i.e., horizontal or diagonal stripe patterns. The prior art machines, however, cannot align either two-dimensional intersecting patterns (such as check patterns) or patterns laying in the sewing direction (such as vertical stripes).